1. Field of the Invention
This invention relates to network devices switches and routers. It is more particularly related to switch stacking where individual switching units are connected in stack for easier management.
2. Prior Art
Network switching devices are connected as stack of switches for easier management. Stackable switches have stack modules to connect with other switches. The stack module has two stacking ports as uplink port and downlink port. Stacking ports of switches are connected to form a stacked switch. The uplink port of a switch (Si) is connected with downlink port of the switch above (Si+1). The uplink port of the top most switch is connected with downlink of the bottom most switch. This forms a closed loop of stacking connections. This connection is shown in diagram FIG. 1.
The closed loop of stacking connections provides redundancy in case of a link or switch failures. If any one of the link failed in stack still the complete stack is manageable through other link. The link failure scenario is shown in diagram FIG. 2.
In practical, more than link failures switch failures are common. Switch failures are expected occasionally due to the complex hardware and software involved. In case of a switch failure in stack, the stack of working switches is still manageable through other redundant link. This switch failure scenario is shown in diagram FIG. 3.
Switch stacking with a redundant link stays connected with no disruption when a failure occurs. This redundant link safeguards against only the first failure. If second or more failures happen the stack gets disrupted. Based on the failure points, the stack might split as multiple stacks or individual switches. This second failure scenario is shown in diagram FIG. 4. Adding further redundant links to handle multiple failures is not a cost effective option. The stacking techniques need to improve to provide better fault tolerance service.